An astronomical refracting telescope will have large angular magnification and high angular resolution when it has an objective lens of ......

Options

A. small focal length and small diameter
B. small focal length and large diameter.
C. large focal length and large diameter.
D. large focal length and small diameter.

Answer

C

Explanation

As magnification of astronomical telescope `=(f_(0))/(f_(e))`
Focal length of objective `(f_(0))` should be greater of focal length of eye piece `(f_(e))` should be smaller and angular resolution = `=(D)/(1.22 lambda)`
`:.` Angular resolution `propD( :.1.22 lambda` is constant)
Hence, high angular resolution can be obtained if diameter (D) by lens is large.